Overview
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Lazy eye

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A "lazy eye" is a childhood condition where the vision does not develop properly. It's known medically as amblyopia.

It happens because one or both eyes are unable to build a strong link to the brain. It usually only affects one eye, and means that the child can see less clearly out of the affected eye and relies more on the "good" eye.

It's estimated that 1 in 50 children develop a lazy eye.

How to tell if your child has a lazy eye

A lazy eye does not usually cause symptoms. Younger children are often unaware that there's anything wrong with their vision and, if they are, they're usually unable to explain what's wrong.

Older children may complain that they cannot see as well through one eye and have problems with reading, writing and drawing.

In some cases, you may notice that one eye looks different from the other. However, this is usually a sign of another condition that could lead to a lazy eye, such as:

a squint – where the weaker eye looks inwards, outwards, upwards or downwards, while the other eye looks forwards

childhood cataracts – cloudy patches that develop in the lens, which sits behind the iris (the coloured part of the eye) and pupil

If your child is too young to tell you how good their vision is, you can check their eyes by covering each eye with your hand, one at a time. They might object to covering the good eye, but they might not mind if you cover the lazy eye.

If they try to push your hand away from one eye but not the other, it may be a sign they can see better out of one eye.

When to get medical advice

Lazy eye is often diagnosed during routine eye tests before parents realise there's a problem.

If you want to be reassured about your child's vision, they can have their eyes tested when they're old enough to attend a sight test at a high-street opticians, which is usually after they're 3 years old.

All newborn babies in the UK have an eye test in the first days of life, and then again at 2 to 3 months old, to look for eyesight problems such as cataracts. Problems like squint and short or long sight may not develop until the child is a few years old.

It's difficult to treat lazy eye after the age of 6, so it's recommended that all children have their vision tested after their fourth birthday. This is the responsibility of your local council, which should organise vision testing for all children between 4 and 5 years of age.

Causes of a lazy eye

The eyes work like a camera. Light passes through the lens of each eye and reaches a light-sensitive layer of tissue at the back of the eye called the retina.

The retina translates the image into nerve signals that are sent to the brain. The brain combines the signals from each eye into a three-dimensional image.

A lazy eye happens when the brain connections responsible for vision are not made properly. To build these connections, during the first 8 years of a child's life, the eye has to "show" the brain a clear image. This allows the brain to build strong pathways for information about vision.

A lazy eye can be caused by:

a reduced amount of light entering the eye

a lack of focus in the eye

confusion between the eyes – where the 2 images aren't the same (such as a squint)

Left untreated, this can lead to the eye's central vision never reaching normal levels.